Always compare MED
With always-compare-med: if the LocalPref, AS_Path length, and origin are the same: ISP-2's route will win in both routers because ISP-1's route is suppressed.
Without always-compare-med, each ISP wins at the their respective BR.
Scenario 2: (Routers A, B and C)
If you add ad Router C with full mess
With always-compare-med: ISP-1's 10.1.0/24 is suppressed and never gets used.
Without always-compare-med: Rc has the choice of ISP-1's and ISP-2's D and will continue through route selection, choosing IGP distance or routerid.
Without taking this to the more complicated cases, the argument that the operational community makes is that "always-compare-med" is problematic